Lecture 14 - Special Senses: Sight and Sound

Question 1

Eyes

Answer 1

Complex, mobile structures that mediates vision

Question 2

Where does photoreception occur?

Answer 2

Retina

Question 3

What does the anterior cavity contain?

Answer 3

Aqueous humour

Question 4

What does posterior cavity contain?

Answer 4

Vitreous humour

Question 5

Extraocular (extrinsic) eye muscles function

Answer 5

Creates eye movements

Question 6

Name the 4 special senses

Answer 6

1. Hearing
2. Taste
3. Smell
4. Sight

Question 7

Pupil

Answer 7

The hole of the eye - absence of tissue

Question 8

Iris

Answer 8

Two smooth muscle components

Question 9

How does the eye control access of light

Answer 9

Dilator layer aids in pupil dilation - allows light to enter

Sphincter layer aids in pupil constriction - area of light is smaller and less light enter

Question 10

Lens function and what does accommodation do?

Answer 10

Lens refracts light, bringing it to a focal point. Accommodation changes the distance focal point by controlling the shape of the lens

Question 11

Ciliary body

Answer 11

Composed of two smooth muscle layers with different fibre orientations (distinct from the iris)

Question 12

What is the retina composed of?

Answer 12

Multi-layered sheet of neurons

Question 13

Process of light from the retina to the brain

Answer 13

1. Light hits the retina
2. Photoreceptors transduce information from light
3. The neural signals goes to the bipolar cells
4. It then enters the retinal ganglion cells (transmitted to the CNS)

Question 14

True or False: Photoreceptors receive light from general points in visual space

Answer 14

False - it only can receive light originating from a distinct point in visual space

Question 15

Macula (fovea centralis)

Answer 15

High density of photoreceptors

Question 16

Optic disc

Answer 16

Region of no photoreceptors - blind spot. It is the entrance and exit for axons and blood vessels. It is a white circle because of myelination

Question 17

What do photoreceptors do and what are the 2 types?

Answer 17

Photoreceptors perform phototransduction, converting photons to Vm signals. Types of photoreceptors:

1. Rods
2. Cones

Question 18

Where does phototransduction occur and what is the function of retinal

Answer 18

Begins in the outer segment with proteins and retinal (vitamin A derivative). Retinal cis-conformation changes to the trans-conformation once light is introduced

Question 19

Rods

Answer 19

Most common in the peripheral retina. Mediates vision in low light and have high sensitivity, but low acuity, meaning it can detect light in a general region

Question 20

Cones and what are the 3 types

Answer 20

Most common in fovea centralis (aka macula) and come in 3 types - gives colour vision. They have low sensitivity but high acuity. The 3 types are:

1. S-cone (small wavelength)
2. M-cone (medium wavelength)
3. L-cone (large wavelength)

Question 21

What are cones connected to

Answer 21

1 cone is connected to 1 bipolar neuron

Question 22

Condition of photoreceptors in the dark

Answer 22

They release NTs constantly - the Na+ channels are open

Question 23

Condition of photoreceptors once light is absorbed

Answer 23

Retinal changes to the trans conformation and activates opsin, leading to the inactivation of Na+ channels and the photoreceptors become hyperpolarized - no NT released

(This is the process of transduction)

Question 24

Process of encoding visual information

Answer 24

1. It begins at the retina, where information from photoreceptors is pooled
2. Then relayed through the thalamus to primary visual cortex (V1), where there is reversed topographic map of visual space

Question 25

What is hearing? What mediates this process?

Answer 25

The detection of sound, or pressure waves in air. The ear mediates this process

Question 26

3 parts of the ear

Answer 26

1. Outer ear
2. Middle ear (where ossicles and tympanum are located)
3. Inner ear (where cochlea is located)

Question 27

Ossicles function

Answer 27

Located in the middle ear, creates vibrations in the fluid of the inner ear at the cochlea, where sound transduction occurs

Question 28

Hair cells

Answer 28

Mediates transduction. Their mobile “hairs” are located within the cochlear duct and are connected to both the basilar membrane and the tectorial membrane

Question 29

How does movement of hair cells affect gated ion channels?

Answer 29

The movement of hair cells relative to the tectorial membrane leads to the opening of mechanically-gated ion channels that depolarize hair cells - larger movements = more depolarization

Question 30

Basilar membrane and sound

Answer 30

The basilar membrane differs in flexibility along its length, so that sounds with different frequency (pitch) cause movements in different parts of the membrane - oval and round window is the base of the membrane; they detect soft, high-pitched sound

Question 31

True or False: cochlea maps space

Answer 31

False - it maps pitch, not space

Question 32

How is location of sound stimulus computed?

Answer 32

It is computed by CNS circuits which compare inputs between the 2 ears

Question 33

Interaural time difference

Answer 33

Sounds are detected first by the ear nearest the stimulus

Question 34

Interaural level difference

Answer 34

The head creates a sound shadow for the farthest ear

Question 35

Tonotopy

Answer 35

The organization according to the pitch (frequency)

Question 36

How is auditory information processed?

Answer 36

Afferent neurons relay auditory information from hair cells to the hindbrain, where it’s process before reaching the forebrain

Question 37

Name 3 types of ion channels found in the hair cells of the cochlea

Answer 37

1. Mechanically-gated ion channels/ mechanosensitive ion channels
2. Voltage-gated channels/voltage-gated Ca2+ channels
3. Leak channels